Effects of elevated concentrations of atmospheric CO2 and tropospheric O3 on leaf litter production and chemistry in trembling aspen and paper birch communities

Human activities are increasing the concentrations of atmospheric carbon dioxide ([CO2]) and tropospheric ozone ([O3]), potentially leading to changes in the quantity and chemical quality of leaf litter inputs to forest soils. Because the quality and quantity of labile and recalcitrant carbon (C) compounds influence forest productivity through changes in soil organic matter content, characterizing changes in leaf litter in response to environmental change is critical to understanding the effects of global change on forests. We assessed the independent and combined effects of elevated [CO2] and elevated [O3] on foliar litter production and chemistry in aspen (Populus tremuloides Michx.) and birch-(Betula papyrifera Marsh.) aspen communities at the Aspen free-air CO2 enrichment (FACE) experiment in Rhinelander, WI. Litter was analyzed for concentrations of C, nitrogen (N), soluble sugars, lipids, lignin, cellulose, hemicellulose and C-based defensive compounds (soluble phenolics and condensed tannins). Concentrations of these chemical compounds in naturally senesced litter were similar in aspen and birch-aspen communities among treatments, except for N, the C:N ratio and lipids. Elevated [CO2] significantly increased C:N (+8.7%), lowered mean litter N concentration (-10.7%) but had no effect on the concentrations of soluble sugars, soluble phenolics and condensed tannins. Elevated [CO2] significantly increased litter biomass production (+33.3%), resulting in significant increases in fluxes of N, soluble sugars, soluble phenolics and condensed tannins to the soil. Elevated [O3] significantly increased litter concentrations of soluble sugars (+78.1%), soluble phenolics (+53.1%) and condensed tannins (+77.2%). There were no significant effects of elevated [CO2] or elevated [O3] on the concentrations of individual C structural carbohydrates (cellulose, hemicellulose and lignin). Elevated [CO2] significantly increased cellulose (+37.4%) input to soil, whereas elevated [O3] significantly reduced hemicellulose and lignin inputs to soil (-22.3 and -31.5%, respectively). The small changes in litter chemistry in response to elevated [CO2] and tropospheric [O3] that we observed, combined with changes in litter biomass production, could significantly alter the inputs of N, soluble sugars, condensed tannins, soluble phenolics, cellulose and lignin to forest soils in the future.     

A comparison of decomposition dynamics among green tree leaves,partially decomposed tree leaf litter and their mixture in a warm temperate forest ecosystem

Decomposition dynamics were compared among green tree leaves, partially decomposed tree leaf litter (i.e., decayed tree leaf litter on forest floor) and a mixture of the two in a warm temperate forest ecosystem in central China to test the influence of litter chemical quality on the degree of decomposition. The study was conducted in situ at two contrasting forest sites, an oak forest dominated by Quercus aliena var. acuteserrata Maxim., and a mixed pine and oak forest dominated by Pinus armandii Franch. and Q. aliena var. acuteserrata. We found marked differences in the rate of decomposition among litter types at both forest sites; the litter decomposition constant, k, was about 39 % greater at the oak forest site and more than 70 % greater at the pine-oak forest site, for green leaves than for partially decomposed leaf litter. The decomposition dynamics and temporal changes in litter chemistry of the three litter types also greatly differed between the two forest sites. At both forest sites, the higher rate of decomposition for the green leaves was associated with a higher nitrogen (N) content and lower carbon to N ratio (C/N) and acid-unhydrolyzable residue to N ratio (AUR/N). We did not find any non-additive effects when mixing green leaves and partially decomposed leaf litter. Our findings support the contention that litter chemical quality is one of the most important determinants of litter decomposition in forest ecosystems at the local or regional scale, but the effect of litter chemical quality on decomposition differs between the contrasting forest types and may vary with the stage of decomposition.     

Indicators of nitrogen conservation in Austrocedrus chilensis forests along a moisture gradient in Argentina

Plant nitrogen conservation which may affect, for instance, rates of litter decomposition, soil N mineralization and N availability is thought to vary along gradients of soil fertility. Since Austrocedrus chilensis is adapted to a wide moisture gradient, we hypothesed that different intensities of N conservation would be found depending on site characteristics. We studied four sites along a moisture gradient in the Andean–Patagonian Region of Argentina, representative of the three A. chilensis forest-types (marginal, compact and mixed forests), and measured the following indicators of N conservation: (i) carbon, nitrogen and C/N ratio in young, mature and senescent leaves, total soil litter and soil; (ii) lignin concentration and lignin/N ratio in senescent leaves and total litter, and (iii) potential soil N mineralization during a 16-week incubation. A. chilensis showed a strong capacity to conserve N: (i) low N concentration in both young and mature leaves (10 and 6.5 g kg⁻¹, respectively); (ii) high N resorption proficiency (5.1 g N kg⁻¹ in senescent leaves) and N use efficiency (200), and (iii) high values of C/N, lignin and lignin/N in senescent leaves (107, 250 g kg⁻¹ and 50, respectively), and total litter (36, 420 g kg⁻¹ and 33, respectively). Some indicators (resorption proficiency, C/N in senescent leaves and lignin/N in total litter) were independent of site characteristics, while others (N and C/N in green leaves and lignin in litter) showed significant differences, suggesting a higher capacity to conserve N in the intermediate sites of the gradient (compact forests). Contrary to expectations, the marginal forest (drier, less fertile soils) showed the lowest values of lignin in litter, the highest N concentrations in green leaves and the highest rates of potential N mineralization.     

Roles of soil chemistry and water availability in site-related delta(13)C variations in French beech forests

The carbon isotopic composition (delta(13)C) of wood and leaf cellulose of beech trees (Fagus sylvatica L.) was studied at 80 sites in northeastern France. We sampled sites with contrasting water balance, depending on soil type and precipitation. We tested the hypothesis that inter-site variations in plant delta(13)C reflect the spatial distribution of soil water availability, and we assessed whether delta(13)C could be used as a bioindicator of soil water availability. Patterns of variation in delta(13)C were compared with estimates of monthly water balance and with other soil characteristics. Between-site variability in delta(13)C was high (2.9 per thousand range in wood cellulose, 2.1 per thousand in leaf cellulose), but variation in water availability appeared to be only a minor factor contributing to this variation in delta(13)C. Unexpectedly, spatial variations in wood and leaf cellulose delta(13)C were significantly and positively related to soil fertility expressed by soil pH (r = 0.42 and 0.43, respectively) and cation content. On average, trees growing on acidic soils displayed 0.5 per thousand lower delta(13)C in both wood and leaf material than trees growing on neutral or calcareous soils. Our initial hypothesis of a strong negative relationship between delta(13)C and site water availability was not confirmed. In the study zone, neither wood nor leaf delta(13)C appeared to be a reliable bioindicator of spatial variations in water availability. Possible causes for the lack of a relationship are discussed. Our findings confirm, under natural conditions, the strong effect of soil fertility on water-use efficiency previously observed in experiments. This effect needs to be considered in isotopic studies involving different sites.     

The influence of trees on soil fertility on two contrasting semi-arid soil types at Matopos,Zimbabwe

An investigation into the influence of indigenous trees on soil fertility was conducted in an area of semi-arid tropical savanna in Zimbabwe on two contrasting soil types: dystrophic savanna soils (sandy soils) and eutrophic savanna soils (fine-textured soils). The study adds further support to the growing literature showing that trees have a positive influence on soil fertility. The study suggests that tree clearance, as advocated in these agropastoral systems, may not necessarily result in long-term benefits. It is argued that the primary mechanism by which soil fertility is improved is through increased litter and soil organic matter compartments under trees. The influence of trees on cation levels is greater on sandy soils than fine-textured soils because the exchange capacity of fine-textured soils is determined largely by soil texture whereas organic matter is the prime determinant of exchange capacity in sandy soils. The present study demonstrates that fertility improvement under trees is not at the expense of fertility decline in the surface soils of the zone around the tree. Leaf quality, as reflected simply in leaf C:N ratio, influences decomposition rates but the activities of termites probably confound any simple relationship. Litter quality of tree species is probably important in determining levels of soil organic matter under canopies, with higher levels under species with lower leaf quality.     

Ozone fumigation of Quercus ilex L. slows down leaf litter decomposition with no detectable change in leaf composition

Context

The evaluation of changes in litter decomposition rate due to increasing trend in tropospheric ozone is an emerging field of investigation, providing relevant information on long-term forest ecosystem sustainability.

Aims

This research aims to clarify the effects of ozone exposure on Quercus ilex leaf chemical composition and decomposition slow down.

Methods

Young plants were fumigated in growth chambers at a cumulative dose of 17.15 ppm h. To assess the fumigation effectiveness, stomatal conductance and net photosynthesis were monitored. Leaves were analysed for C, N, S, Ca, Mg, K, Fe, Zn, Mn, total soluble sugars, starch, acid-detergent fibre (ADF), lignin and cellulose prior to the incubation in litter bags in mesocosms, and during decomposition along 395 days.

Results

Ozone-exposed leaves showed a significant reduction in net photosynthesis and stomatal conductance but did not differ from control leaves in all the chemical parameters analysed. Nevertheless, leaf decomposition rate was lower in treated leaves. The main differences between the models describing the mass loss in exposed and control leaves were played by ADF for exposed leaves and by lignin for control leaves, as well as by N, that showed a greater contribution in the model for the exposed leaves.

Conclusion

Ozone fumigation of Q. ilex results in leaf litter decomposition slowing down, mainly due to ADF joint dynamics with the other variables describing mass decay, even if no detectable changes in initial leaf composition occur.     

Indirect effects of precipitation variation on the decomposition process of Mongolian oak (Quercus mongolica) leaf litter

The effect of precipitation variation on the chemistry of Mongolian oak (Quercus mongolica) leaf litters was examined by analyzing litters of Mongolia oak saplings under four precipitation gradients. The decomposing process of these leaf litters in the Mongolian oak dominated forest was assessed using litter bag method. Compared with the litters of the Mongolian oak saplings from the natural precipitation site (A), litters produced by Mongolian oak from the driest precipitation gradient (A₄₅₀) had significantly higher concentrations of nitrogen (N), phosphorus (P) and potassium (K) while lower acid-insoluble fraction (AIF) concentration. The decomposition study showed that A₄₅₀ exhibited significantly higher decomposition rate, mineralization rates of N, P and K as well as much shorter N and P net immobilization periods. On the contrary, litters produced by seedlings from wettest gradient (A₈₅₀) showed a totally opposite pattern. Litters from saplings that received comparable precipitation (A₆₅₀) to those at the natural site (A) had significantly higher N concentration and faster decomposition rate as well as release rates of N, P and K. The mass loss patterns for the four litter types fitted the exponential model and the decay constant (k) can be well predicted by initial AIF/N. During the decomposition period, N concentration was best related to the percentage of mass remaining of the litters with relatively higher AIF concentrations and lower N concentrations, but the percentage of mass remaining of litters with lower AIF concentrations and higher N concentrations correlates strongly with AIF con centration. Our study proved that changes in precipitation significantly altered the litter quality, and therefore indirectly changed the decay process of leaf litters. __________ Translated from Chinese Journal of Applied Ecology, 2007, 18(2): 261–266 [译自: 应用生态学报]     

Tree effects on the chemical topsoil features of oak, beech and pine forests

We aimed to study tree effects on the chemical properties of forest soils. We compared soil features of three types of forest ecosystems, each with four stands (replicates): beech forests (Fagus sylvatica), oak forests (dominated by Quercus pyrenaica) and pine plantations (Pinus sylvestris). Five samples from the top 10 cm of soil were taken per stand, from which pH, organic matter content (O.M.), total nitrogen (N) and available calcium (Ca²⁺), magnesium (Mg²⁺), potassium (K⁺) and sodium (Na⁺) were determined. Litter layer depth was measured at each soil sampling point. We also measured tree density and crown diameters at each stand. Our results indicated that soil samples from the four pine plantation stands were more similar while oak and beech stands were characterised by great variability in terms of soil properties and leaf litter depth. Although the identity of the dominant tree species significantly influenced several topsoil chemical properties (increase in pH and available cations in oak forests and higher organic matter and total nitrogen in beech and pine ecosystems), there were other important factors affecting soil features that may be taken under consideration. Differences between soil properties of the three types of forest ecosystems were mainly related to the characteristics of the litter layer and less related to the tree layer structure. Finally, the establishment of pine plantations in naturally deciduous tree areas made the topsoil features more homogeneous.     

气候和枯落物质量对印度东部亚热带森林凋落叶分解和营养回归的影响(英文)

为了评价印度东部曼尼普尔亚热带橡树混交林中的土壤养分收支平衡情况,研究了全年不同月份的3个主要树种,枹栎(Quercus serrata)、木荷(Schima wallichi)和滇石栎(Lithocarpus dealbata)的枯落物分解和营养回归情况。印度东部橡树林是生产柞蚕丝的重要经济树种。林下2-7月月枯落物为25.6 g·m-2(7月)和198.0 g·m-2(2月),年枯落物为1093 8g·m-2。在初始月(11月3),滇石栎森林壤土的氮和碳浓度最高,其次是在枹栎林。最低的是木荷林。但就木质素和纤维素含而言,木荷林中的最高,其次是袍栎林和滇石栎林。滇石栎林(k=0.54)具有较高的枯落物分解率,这与月初枯落物中含有较高的氮和碳浓度以及低含量的纤维素相符合。然而,在木荷森林中枯落物分解率低,是与月初时森林土中具有低浓度氮和碳及高浓度木质素和纤维素相符合。在不同月份,剩余的生物量与木质素、碳、碳氮比和纤维素含量呈正相关,但与氮含量呈负相关。由于环境条件的影响,在寒冷和冬季枯落物分解率最低,而在雨季枯落物分解率最高。图3表5参52。     

Decomposition of needle/leaf litter from Scots pine, black cherry, common oak and European beech at a conurbation forest site

Litter decomposition was studied for 2 years in a mixed forest serving as a water protection area (Rhine-Neckar conurbation, SW Germany). Two experiments differing in initial dry weight equivalent in litterbags were set up: one to compare decomposition of European beech leaves (Fagus sylvatica) with common oak leaves (Quercus robur), and the other comparing decomposition of Scots pine needles (Pinus sylvestris) with black cherry leaves (Prunus serotina Ehrh.), respectively. Mass losses were greater for oak litter than for beech (75.0 versus 34.6%), and for cherry litter than for pine (94.6 versus 68.3%). In both experiments, a strong initial loss of soluble compounds occurred. The changes in litter N and P concentrations and the decrease in C-to-N ratio coincided with changes in residual mass. However, neither tannin and phenolic concentrations nor NMR could explain the pronounced variation in mass loss after 2 years. Differences in litter palatability and toughness, nutrient contents and other organic compounds may be responsible for the considerable differences in residual mass between litter types. The fast decay of black cherry leaves appears to play a major role in the present humus dynamics at the studied site. Since black cherry has a high N demand, which is mainly met by root uptake from the forest floor, this species is crucial for internal N cycling at this conurbation forest site. These effects together may significantly contribute to prevent nitrate leaching from the forest ecosystem which is subject to a continuous N deposition on an elevated level.     

Responses of decomposition of green leaves and leaf litter to stand density,N and P additions in <Emphasis Type="Italic">Acacia auriculaeformis</Emphasis> stands

The effects of nitrogen (N), phosphorus (P) and N?+?P additions on the decomposition of green leaves and leaf litter were studied over 2 years using the litterbag technique in Acacia auriculaeformis stands with different densities in southern China. The green leaves and leaf litter were treated with four fertility treatments: control, N addition, P addition and N?+?P addition to test the effect of stand density and fertility on the decomposition of green leaves and leaf litter. The mean percentage of mass remaining (PMR) of green leaves and leaf litter significantly decreased with increasing density. Nitrogen and N?+?P additions had a negative effect on PMR, whereas the addition of P had a positive effect. The rapid decomposition of green leaves was associated with a higher N and P content and a lower N/P ratio, indicating a likely P limitation for A. auriculaeformis stands. Our results imply that stand density associated with canopy openness can impact litter decomposition, and P is an important control factor on litter decomposition in A. auriculaeformis stands.     

Fate of nitrogen released from 15N-labeled litter in European beech forests

The decomposition and fate of 15N-labeled beech litter was monitored in three European beech (Fagus sylvatica L.) forests (Aubure, France; Ebrach, Germany; and Collelongo, Italy) for 3 years. Circular plots around single beech trees were isolated from roots of neighboring trees by soil trenching, and annual litterfall was replaced by 15N-labeled litter. Nitrogen was continuously released from the decomposing litter. However, over a 2-year period, this release was balanced by the incorporation of exogenous N. Released N accumulated mainly at the soil surface and in the topsoil. Microbial biomass remained almost constant during the experiment at all sites except for considerably lower values at Ebrach. The 15N enrichment of the microbial biomass increased strongly during the first year and then remained stable. The 15N released from the decomposing litter was rapidly detected in roots and leaves of the beech trees, increasing regularly and linearly over the course of the experiment. The uptake of litter-released 15N by the trees was reduced under conditions that reduced tree growth. Under these conditions, leaves and fine roots were the dominant N sinks, and little N was allocated to other plant parts. By contrast, N uptake and N allocation from leaves to stem and bark tissues increased when tree growth was enhanced. Budgets for 15N showed that 2 to 4% of litter-released N was incorporated into the trees, about 35% remained in the litter and about 50% reached the topsoil.     

Canopy cover effects on mass loss, and nitrogen and phosphorus dynamics from decomposing litter in oak and pine stands in northern Lower Michigan

Patterns of litter decomposition and nitrogen (N) and phosphorus (P) release in relation to various levels of canopy cover were examined using litterbags placed on the forest floor of northern red oak (Quercus rubra L.) and red pine (Pinus resinosa Ait.) stands in northern Lower Michigan, USA. A series of experimental plots consisted of four levels of canopy cover treatments, i.e. clearcut, 25% (50% during first sampling year), 75%, and uncut. Mass loss from decomposing leaves was higher for oak leaves in red oak stands (approximately 60% loss of the original mass) than for pine needles in red pine stands (approximately 40% loss of the original mass) during the 2 year study period. Leaf mass loss in the clearcut red oak treatment was significantly higher than in the uncut red oak treatment. In contrast, no canopy cover effects on litter mass loss were found in red pine stands. Nitrogen concentrations in decomposing litter increased during the 2 year period in all canopy cover treatments in both stand types, but they did not differ significantly among canopy cover treatments. These results indicate that various levels of red oak and red pine canopy removal generally have a minor impact on litter decomposition and nutrient (N and P) release during the first 2 years following canopy manipulation, except in red oak clearcuts.     

Contrasting distribution and seasonal dynamics of carbohydrate reserves in stem wood of adult ring-porous sessile oak and diffuse-porous beech trees

We tested the hypothesis that broad-leaved forest species with contrasting wood anatomy and hydraulic system (ring-porous versus diffuse-porous) also differ in distribution and seasonal dynamics of carbohydrate reserves in stem wood. Total nonstructural carbohydrate (TNC) reserves (starch and sugars) were measured enzymatically in the 10 youngest stem xylem rings of adult oak (Quercus petraea (Matt.) Liebl.) and beech (Fagus sylvatica L.) trees during an annual cycle. Radial distribution of carbohydrates was investigated according to ring age. On all dates, oak trees had twofold higher TNC concentration than beech trees (41 versus 23 mg g(DM)(-1)), with starch accounting for the high TNC concentration in oak. Seasonal dynamics of TNC concentration were significantly (P < 0.05) more pronounced in oak (20-64 mg TNC g(DM)(-1)) than in beech (17-34 mg TNC g(DM)(-1)). A marked decrease in TNC concentration was observed in oak trees during bud burst and early wood growth, whereas seasonal fluctuations in TNC concentrations in beech trees were small. The radial distribution of TNC based on ring age differed between species: TNC was restricted to the sapwood rings in oak, whereas in beech, it was distributed throughout the wood from the outermost sapwood ring to the pith. Although the high TNC concentrations in the outermost rings accounted for most of the observed seasonal pattern, all of the 10 youngest xylem rings analyzed participated in the seasonal dynamics of TNC in beech trees. The innermost sapwood rings of oak trees had low TNC concentrations. Stem growth and accumulation of carbon reserves occurred concomitantly during the first part of the season, when there was no soil water deficit. When soil water content was depleted, stem growth ceased in both species, whereas TNC accumulation was negligibly affected and continued until leaf fall. The contrasting dynamics and distribution of carbohydrate reserves in oak and beech are discussed with reference to differences in phenology, early spring growth and hydraulic properties between ring-porous trees and diffuse-porous trees.     

Plant limiting nutrients in Andean-Patagonian woody species: Effects of interannual rainfall variation,soil fertility and mycorrhizal infection

Andean-Patagonian forests are especially interesting for the study of N and P limitation because they receive minimal atmospheric pollution, have little influence of vascular N-fixing species, and grow on volcanic soils that retain P. In a previous study of 10 woody species (four broad-leaved deciduous species, three broad-leaved evergreens and three conifers) conducted during an exceptionally dry year in NW Patagonia, and on the basis of nutrient resorption efficiency and proficiency, we suggested that N was the most limiting nutrient except for the broad-leaved evergreen Lomatia hirsuta. In the present work, we compared patterns of nutrient limitation during a dry and a wet year, quantified the percentage of mycorrhizal infection, and related mycorrhizal behavior and nutrient limitation to soil fertility. We used N and P concentrations in green leaves as indicators of nutrient requirements, and N and P concentrations in senescent leaves (resorption proficiency) and the N/P ratio in green leaves as indicators of nutrient limitation. We also determined leaf mass area (LMA) and lignin concentration as indicators of structural and chemical defences. From previous works, the following soil fertility indicators were included: pH, organic C, total N, exchangeable cations, Olsen-P, potential N mineralization (pNmin) and N retained in microbial biomass (N-MB). Nitrogen, P and lignin concentrations in green and senescent leaves did not differ significantly between the dry and the wet year either by species or by functional groups. Most species behaved as N-proficient and P-non-proficient; this together with values of foliar N/P ratios lower than 14–16 confirmed N limitation in these forests. The only species limited by P but not by N was L. hirsuta (1.0–1.1% N in senescent leaves, N/P ratio = 21–23), a non-mycorrhizal species with cluster roots. The lack of P limitation in the other species was probably related to the high percentages of infection with arbuscular mycorrhizae (80–90% in Maytenus boaria and the conifers Araucaria araucana, Austrocedrus chilensis and Fitzroya cupressoides), and ectomycorrhizae (73–79% in five Nothofagus species). Nitrogen and P requirements were positively correlated among themselves and negatively with lignin and LMA. Soil fertility was positively correlated with nutrient requirements and negatively with lignin and LMA. Conifers had lower N and P requirements, higher LMA, lower foliar N/P ratio and grew on soils of lower soil N dynamics (lower pNmin and N-MB) than ectomycorrhizae-associated species.     

Interactions in decomposition and N mineralization between tropical legume residue components

In situ produced plant residues contain a mixture of different plant components of varying quality. To assess synergistic or antagonistic interactions occurring during the decomposition and mineralization of such mixtures, individual plant parts (stems, leaves, leaf litter and roots) or the mixture of stems, leaves and leaf litter of the agroforestry species pigeonpea (Cajanus cajan) or of crop residues of peanut (Arachis hypogaea) or of the weed hairy indigo (Indigofera hirsuta) were incubated in pots for 19 weeks. Periodically, remaining plant residues were sieved out (>2 mm), weighed and N content as well as soil mineral N determined. Above- and below-ground residues of peanut decomposed fastest and showed the largest N release in agreement with their high N concentration and low-acid detergent fibre (ADF) : N ratio. Hairy indigo was hypothesized to be of lower quality than pigeonpea because of its high-polyphenol content. However, it decomposed faster than pigeonpea, largely because of the higher N and lower lignin concentration of its components. Ranking of individual plant components for N mineralization resulted in the following pattern, leaves > leaf litter > roots > stems. In mixtures of the different plant components a similar species order in decomposition was obtained, e.g. peanut > hairy indigo > pigeonpea. The amount of N released from the mixture was dominated by stem material that comprised 46–61% of the mixture. The interactions in mixtures were relatively small for peanut (generally high-quality components) as well as for pigeonpea (low proportion of high-quality components, i.e. N rich leaf material). However, a positive interaction occurred during later stages of N mineralization in the mixture of hairy indigo as it had a significant proportion of N rich components and absence of highly reactive polyphenols. Thus, for plants with low to intermediate chemical quality attributes, manipulating plant composition (e.g. by varying harvest age, affecting stem and leaf proportions) will be important to obtain significant interactions during decomposition when its components are mixed.     

Physiological and phenological responses of oak seedlings to oak forest soil in the absence of trees

Established trees influence the growth and physiology of seedlings by altering above- and belowground conditions; however, tree influences on seedling physiology via belowground interactions are not well understood. We used soil transfers to an open field to examine the belowground influences of a Quercus ellipsoidalis E.J.Hill dominated forest on Q. ellipsoidalis seedling mycorrhizal infection, nutrient uptake, growth and photosynthesis over three years. After two years, seedlings planted with large quantities of forest soil (HF treatment) had greater leaf mass and foliar N concentrations than seedlings receiving smaller quantities of forest soil (LF) and control treatments. Mycorrhizal infection was greater in the HF treatment after one year compared with the LF and control treatments, with a positive correlation of foliar N and mycorrhizal infection in Year 2. There were marked effects of treatments on seedling spring phenology with HF seedlings breaking bud up to 17 days earlier than seedlings in the other treatments. The HF seedlings also had more rapid leaf expansion and larger leaves, and an increase in net photosynthetic rates. These results highlight complex linkages between above- and belowground physiology: forest soil had substantial effects on seedling physiology, including traits such as phenology that have previously been considered to be under aboveground control. Belowground influences of trees on conspecific seedlings may play a critical role in early seedling establishment.     

Changes in soil organic carbon fractions in a tropical Acrisol as influenced by the addition of different residue materials

Residues of Leucaena (Leucaena leucocephala (L), Senna siamea (S) and maize stover (M) were tested to evaluate their effect on soil organic matter accumulation and composition under sub-humid tropical conditions. On an Imperata cylindrica (I) dominated grass fallow, a total amount of 30?Mg?ha^?1 DM were applied within 18?months. Two months after the last application, changes in the light and heavy soil organic carbon fraction (LF and HF) and in the total soil organic carbon content (LF?+?HF) in the topsoil were observed. All organic materials increased the proportion of the LF fraction in the soil significantly. The increase in HF was 39 to 51% of the increase in total organic carbon, depending on the source of the organic material. The potential of the tested organic materials to increase total soil organic carbon content (including all soil organic carbon fractions) was in the order L?>?S?>?M?>?I, whereas the order of increase of the HF fraction was L?=?S?>?I?>?M. Cation exchange capacity of the newly formed heavy soil organic carbon was highest with L and lowest with M. Ranking of the transformation efficiency of applied plant residues into the heavy soil organic carbon fraction was I?>?L?=?S?>?M. Transformation efficiency of the residues could neither be explained by lignin nor lignin/N ratio, but rather by extractable polyphenols (Folin?CDenis extraction). The results show that accumulation of the HF fraction in tropical soils is feasible through the application of large quantities of plant residues, but depends strongly on the composition of the applied materials.     

Modelling moisture-related mechanical properties of wood Part I: Properties of the wood constituents

Summary By starting with simple concepts of the molecular structure and building up through the various levels of organisation in the wood cell wall it is possible to construct a model that simultaneously predicts the variation with moisture content change of both the longitudinal Young's modulus and longitudinal shrinkage of wood. To do this it is first necessary to define the stiffness and swelling characteristics of the lignin, hemicellulose and cellulose constituents of the wood as moisture content changes. It is suggested here that it is the bound fraction of the sorbed water that is responsible for the changes in swelling stress as well as for change in stiffness in the lignin and hemicellulose. The magnitudes of the stiffness of each of the constituents appear to be quite closely circumscribed by experimental values for longitudinal Young's modulus and shrinkage of wood and it is apparent that the stiffness characteristics of the in situ constituents are compatible with available experimental evidence for extracted lignin and hemicellulose and for native cellulose.     

Influences of nitrogen and phosphorus addition on polyphenol oxidase activity in a forested Andisol

Increased atmospheric N deposition could suppress plant litter decomposition, due to the P limitation for soil microorganisms in Japanese forested Andisols with a high P sorption capacity. To explore this possibility, we used a laboratory incubation experiment to study the influence of N addition on β-d-glucosidase and polyphenol oxidase activities, which are important for cellulose and lignin degradation, respectively, in an Andisol with larch (Larix kaempferi) leaf litter. The addition of N increased the β-d-glucosidase activity, whereas it decreased the polyphenol oxidase activity in the soil. However, the addition of both N and P increased the polyphenol oxidase activity in the soil, suggesting the possibility of; (1) an inferior competitive ability of polyphenol oxidase-producing microorganisms under nutrient-rich conditions and; of (2) their P limitation through competition in the Andisol.